Moon Phases/Transcript
Transcript Text reads: The Mysteries of Life with Tim and Moby Tim is in his bedroom at night with his lights out. A lamp in the shape of the sun is on a pole in the center of his room. Tim is wearing a model of the earth, with his head, hands, and legs poking out. He orbits around the sun-shaped lamp, facing it as the theme from "2001: A Space Odyssey" plays. Moby opens the bedroom door and switches on the bedroom light. MOBY: Beep. Moby stares at Tim. Both of them look uncomfortable. TIM: It's, um... not what it looks like. Tim reads from a typed letter. TIM: To Tim and Moby, I've heard the moon waxes and wanes. What does that mean? From, Devan. Moby stands next to Tim. Tim is still dressed as the Darth, and Moby is now dressed as the moon. TIM: Hey, Devan. Here on Earth, the moon doesn't always look like a perfect circle in the sky. Its appearance changes over time. It waxes, or grows, and wanes, or shrinks. An animation shows the moon in space as it waxes and wanes several times. Its appearance changes as Tim describes, with greater and lesser parts of it lit by the sun. TIM: The moon goes through a cycle of different shapes, or phases, over the course of about one month. A chart shows the moon's phase each night over the course of a 31 day month. It gradually changes from being completely dark, to partially dark, to a fully lit, and back again. TIM: In fact, the whole concept of months is based on this cycle. MOBY: Beep. TIM: Believe it or not, shadows have nothing to do with the moon's phases. You might be picturing the earth-moon-sun system like this. An animation shows the moon orbiting the earth and the earth orbiting the sun, with all motion occurring on the same plane. TIM: But if everything were all flat like this, you'd get a solar eclipse every time the moon was here. The animation shows the moon directly between the earth and the sun. A second image shows what the sun would look like from the earth's surface with the moon in that position. There would be a complete solar eclipse. TIM: And a lunar eclipse every time it was here. An additional animation shows the earth directly between the sun and the moon. It illustrates the complete lunar eclipse that this would cause. TIM: In reality, eclipses are pretty rare. MOBY: Beep. TIM: Okay, let's see how it really looks. The moon's orbit around the earth is tilted about five degrees from our orbit around the sun. So, in most cases, any shadows cast by the earth and moon completely miss each other. An animation shows the earth, sun, and moon in space. Dotted lines indicate the tilt Tim describes, and images show the shadows caused by that tilt. TIM: Now that we've cleared that up, let's see the phases in action. The light in Tim's room switches off. The sun-shaped lamp is shining. Tim stands on a chair, dressed as the earth. Moby, dressed as the moon, stands between the lamp and Tim. TIM: Like the earth, half the moon's surface is always lit by the sun, and half is in the dark. An overhead view shows Moby/Moon and Tim/Earth, lit as Tim describes. TIM: But the amount of that bright side that we can see changes as the Moon moves through its orbit. Moby/Moon orbits Tim/Earth, facing the sun-shaped lamp the entire time. Half of Moby's costume is lit by the lamp. Doing this illustrates how the moon's phases appear from Earth's surface. TIM: When the moon is directly between the earth and sun, forming a straight line, the entire bright side is facing away from us, so we see nothing at all, or at best a dark disk. An image shows the configuration of the sun, moon, and earth that Tim describes. A second image shows that the moon appears completely dark when viewed from the earth's surface. TIM: This phase is called the new moon. MOBY: Beep. Moby ignites his rocket shoes. He floats slowly past Tim/Earth, with more of Moby/Moon's surface lighting up. TIM: Right. As you move along in your orbit, more and more of your bright side becomes visible to me. In other words, the moon is waxing. Phases where you can see less than half of the bright side are called crescent moons. An animation shows four different crescent moons in the night sky. TIM: When the moon has completed one quarter of its orbit around Earth, we can see half of its illuminated side. Moby/Moon and Tim/Earth demonstrate what Tim describes. TIM: Astronomers call this the first quarter moon, but it's more commonly known as a half-moon. An image shows the moon in the sky. Its left half is dark, and its right half is brightly lit. TIM: Once you can see more than half, it's called a gibbous moon. An image shows a moon with about two-thirds of its illuminated side visible. TIM: When the moon and the sun are on opposite sides of the earth, the entire bright side of the moon is facing toward us. So, we see a shiny full moon. Images show the sun, moon, and earth positioned as Tim describes them. The entire illuminated side of the moon is visible from earth. TIM: Beautiful, isn't it? MOBY: Beep. TIM: Now, as the moon continues its orbit, we see less and less of its lit side. Moby/Moon continues his orbit around Tim/Earth, showing less of its lit side. TIM: It passes through the waning gibbous phases, and when it completes three quarters of its orbit, the other half of the bright side becomes visible as the third quarter moon. One half of the illuminated side of the moon is visible, but now it is the left half, not the right. TIM: Next, it passes through the waning crescent phases. And finally, the moon comes back around to where it started, and we're back to a new moon. An animation shows the final phases as Tim describes them. MOBY: Beep. TIM: The amount of time between one new moon and the next is called a lunar month, and it's about 29.5 days. A calendar chart of the moon's phases illustrates the period Tim describes. TIM: But the time it takes for the moon to make one complete orbit around Earth is actually a bit less, about 27.3 days. MOBY: Beep. TIM: Well, remember, while the moon travels around the earth, the earth is moving around the sun. So, when the moon finishes one complete circuit, the earth has moved quite a bit. The three bodies now form an angle instead of a straight line, so we can still see a crescent moon. It takes the moon about two days to catch up and get into new moon position again. An animation shows the motion of the moon, earth, and sun as Tim describes. Dotted lines indicate the moon's orbit around Earth and Earth's distance from the sun. TIM: Okay. Now we can finally put these costumes away. Tim looks over at Moby. Moby is dressed as the Death Star from the Star Wars films. TIM: Oh, no. That's no moon. Moby grins, and green laser rays shoot from him. TIM: Aargh! Tim runs. Category:BrainPOP Transcripts Category:BrainPOP Science Transcripts